5 Answers
5

"How and when did the letter Z become to be associated with sleeping?"

First of all, zzzz (or z-z-z-z) is sound of snoring, from at least 1918. (Sometimes "a tiny saw cutting through a log" [1948] would be used, and both the snore and saw would make the same z-z-z-z sound.) Over time, this became associated with sleep in general, but most comic reference books (e.g. 2006's KA-BOOM! A Dictionary of Comic Book Words, Symbols & Onomatopoeia, 2008's Comic books: how the industry works) still mainly associate it with snoring.

The reason zzz came into being is that the
comic strip artists just couldn’t
represent sleeping with much. ... As
the sounds made while sleeping are
quite difficult to represent with
letters, the artists chose zzz,
because it best represents the sound
... In fact it has made itself into
its own meaning - it no longer needs
explanation and is generally accepted
world wide as a representation of
sleeping. The reason it even became
what it now is, is almost lost, such
as the meaning of the wrong end of the
stick. I’ll let you figure that one
out.

The earliest references I found connect zzzz with snoring, including an explanation that says snoring is indicated by zzzz.

Contact point by the University of the Pacific, School of Dentistry in 1927:

ZZZZZZ (snoring)— Heard during
lecture. 2. The Scolenius Medius. the
largest and longest of the three
Scoleni. arises from the posterior
tubercle of the transverse processes
of the lower six cervical vertebrae,
and descending along, ...

This may sound crazy, but even in the
breeze the zigzag cages will seem
cozy. They will all be the right kind
and size. And at night I will play a
zither to help all the animals go to
sleep and snooze, Zzzzz

It is a convention in American comics
that the sound of a snore can be
reduced to a single letter Z. Thus a
speech bubble with this letter
standing all alone (again, drawn by
hand rather than a font type) means
the character is sleeping in most
humorous comics. This can be seen, for
instance, in Charles Schulz's Peanuts
comic strips.

Being such a long-established device,
the Z-bubble does not even imply that
the character is snoring anymore, but
just sleeping. Jim Davis has based
some jokes starring Garfield upon this
technique; for example, in one strip,
Garfield is unable to sleep because
his Z-bubble is pointing in the wrong
direction. When he grabs the bubble's
tail to make it point at himself, he
falls asleep.

Originally, the resemblance between
the 'z' sound and that of a snore
seemed exclusive to the English
language, but the spread of American
comics has made it a frequent feature
in other countries. An exception to
this is in Japanese manga, where the
usual symbol for sleep is a large
bubble coming out of the character's
nose.

I have just discovered this question and am surprised that more reference has not been made to the word snooze. There is a passing reference in the accepted answer but, on checking, this word dates back to 1789 and is described as 'a cant word, echoic of a snore.' Cartoons through the years seem to have extended snooze or borrowed the latter zzz sound which, by default, has become its representation. My theory, anyway!

Zzzzz seems to more closely match the sound of a buzzing fly, IMO, but I get it. Do you have any insight on to when it was first used?
–
Scott MitchellMay 25 '11 at 22:54

@Scott Mitchell: The only thing I've found after 30 minutes.
–
user8568May 25 '11 at 23:26

3

I'm not convinced this very pat explanation is sufficient. The person who added [citation needed] to the Wikipedia article agrees. I've never heard any snoring that sounds like [zzzz]. The sound requires conscious tongue positioning and vocal cord vibration to produce, which is difficult to do while unconscious.
–
nohat♦May 26 '11 at 4:05

1

I have never heard a snoring person with anything close to a Z, and I have lived with some EPIC snorers. Epic I tell you. It is more like "snnCHHhkkkk,,,phsawwww" :)
–
horatioMay 26 '11 at 18:16

Someone came close to the correct answer, but failed to put 2 and 2 together. The letter Z represents the motion of someone sawing wood with a hand saw, which sounds close to the sound of someone snoring. Originally someone "sawing wood" was the description given to the sound when snoring, often accompanied by an image of sawing wood or a hand motion (in the Z formation) of someone sawing wood. Later it was condensed and simplified just by using the letter Z or a series of Z's (ZZZZZZ = Sawing Wood = Snoring Sound)

@Matthew: the brain wave is particular important when people refers to sleep.
–
Xiè JìléiMay 27 '11 at 0:55

It's a matter of perspective, I guess. Of the dozen or so clinical uses in the Wikipedia article you linked to, sleep isn't even listed. But it's fine, I don't need to convince you, I just wanted to point out that "people send out brain waves when they are sleeping" makes it sound like EEG activity only happens when you're sleeping; the fact is that it happens all the time.
–
Matthew FrederickMay 27 '11 at 1:39

@Matthew: Yes, EEG happens all the time. But when awake, people send out brain waves, doing their work, study and play. But when sleep, people do only send out brain waves.
–
Xiè JìléiMay 27 '11 at 1:47

I think what he's saying is that brain electrical activity is pretty much the only activity during sleep. Hence the electrical symbol (lightning strike) which resembles and is substituted with is Z. Like dreams happening due to (electrical) brain activity.
–
ChrisNov 20 '12 at 3:12